Electrical System

90-863758070 APRIL 2008 Page 8A-1

8A

Electrical SystemSection 8A - Electrical System

Table of Contents

Finding Other Diagrams...................................8A-2General Information.........................................8A-2Precautions......................................................8A-2Industry Standards and Regulations................8A-3Battery and Battery Cables Requirements.......8A-4

Battery .....................................................8A-4Battery Cables..........................................8A-5

Electrical Connections.....................................8A-6SmartCraft Product...................................8A-6Engine Harness........................................8A-6Engine Connections..................................8A-9Continuity Wire Connection......................8A-9Accessories............................................8A-11

Audio Warning System..................................8A-11Audio Warning System without EmissionsControl....................................................8A-11Audio Warning System with EmissionsControl....................................................8A-11

Multiple EFI Engine Battery Precautions.......8A-13Situation..................................................8A-13Recommendations..................................8A-13

Battery Switch................................................8A-14Finding Other Diagrams.................................8A-14Power Harness..............................................8A-14Battery Isolator...............................................8A-15

Battery Isolator Diagram.........................8A-16

Electrical System

Page 8A-2 90-863758070 APRIL 2008

Lubricant, Sealant, AdhesivesTube Ref No. Description Where Used Part No.

25 Liquid Neoprene All electrical connections except the battery 92- 25711 3

Finding Other DiagramsNOTICE

Refer to the appropriate Mercury MerCruiser Diagram Binder for wiring diagrams or other diagrams not foundin this manual.

General InformationThis section covers the engine portion of the electrical system. For instrumentation relatedinformation, see Section 9.The electrical system is a 12‑volt, negative ground system. High output (65/72 amp)alternators are included as standard equipment. Their high output design helps ensure thatthe battery remains fully charged for trouble‑free starting, while providing extra capacity tohandle the accessories used on today's boats. All alternators are equipped with an externalsensing circuit to maintain the battery at the optimum voltage level, while providing for theuse of a battery isolator, if desired. Special high‑capacity marine starters are also employedto provide reliable starting and long life in the rigorous marine environment. MercuryMerCruiser starters, alternators, distributors, solenoids, circuit breakers, fuses, and othercomponents that could generate a spark comply with external ignition standards andregulations to prevent the ignition of combustible fumes in the engine compartment shouldthey exist. These components should not be confused with standard automotivecomponents, which typically do not have this provision. The electrical system is equippedwith numerous overcurrent protection devices (circuit breakers, fuses) to protect the engineagainst shorts and overloads. See Wiring Diagrams for the location of these devices. Theengine compartment should be designed to allow access to these components.IMPORTANT: No one component is more important in ensuring the reliability of theelectrical system than is the battery and related hardware. The installation of the batteryand cables is the responsibility of the boat manufacturer. The guidelines outlined in thissection must be carefully followed when selecting and installing these items.

Precautions! WARNING

Avoid fire or explosion hazard. Electrical, ignition, and fuel system components onMercury Marine products comply with federal and international standards to minimize riskof fire or explosion. Do not use replacement electrical or fuel system components that donot comply with these standards. When servicing the electrical and fuel systems, properlyinstall and tighten all components.

! WARNINGPerforming service or maintenance without first disconnecting the battery can causeproduct damage, personal injury, or death due to fire, explosion, electrical shock, orunexpected engine starting. Always disconnect the battery cables from the battery beforemaintaining, servicing, installing, or removing engine or drive components.

Electrical System

90-863758070 APRIL 2008 Page 8A-3

! CAUTIONFailure to protect wiring with an appropriate fuse can damage the wiring and start a fire.When installing any accesories, we recommend using a Mercury accessory kit. Alwaysuse the appropriate fuse to protect wiring.

IMPORTANT: Refer to the following precautions when working on or around the electricalharness, or when adding other electrical accessories, to avoid damage to the electricalsystem.• Do not tap accessories into the engine harness.• Do not puncture wires for testing (probing).• Do not reverse the battery leads.• Do not splice wires into the harness.• Do not attempt diagnostics without the proper, approved service tools.IMPORTANT: The accessory wire in the 14‑pin harness will not support amperage inexcess of 15 amps. Refer to Quicksilver Accessories for an optional relay kit that willaccommodate a higher amperage draw.

Industry Standards and Regulations! WARNING

Improper design and installation of the electrical system can result in serious injury ordeath. Adhere to all applicable marine regulations (United States Coast Guard [USCG],European Union–Recreational Craft Directive [EU‑RCD], etc.) and the standards theyreference (American Boat and Yacht Council [ABYC], Society of Automotive Engineers[SAE], International Standards Organization [ISO], etc.) for the market in which the boatwill be sold.

The following excerpts from the ABYC Standards should be observed when designing andinstalling the electrical system. These are just a few of the more fundamental standardsthat, if observed, can significantly improve the overall reliability and durability of the boatand engine package. The list is not intended to be all‑inclusive, and should not be used asa substitute for reading the standards.• Current carrying conductors shall be routed as high as practical above bilge water level

and other areas where the water may accumulate. The wiring and connections mustbe water‑tight.

• Conductors should be routed as far away as practical from exhaust pipes and otherheat sources. Unless an equivalent thermal barrier is provided, a clearance of 51 mm(2 in.) should be provided between conductors and the water cooled MercuryMerCruiser exhaust system components.

• Conductors that may be exposed to physical damage shall be protected by self‑drainingloom, conduit, tape, raceways, or other equivalent protection.

• Conductors passing through bulkheads or structural members shall be protected toavoid insulation damage such as chafing by using grommets.

• Conductors should be routed to clear sources of chafing such as steering cable andlinkages, throttle connections, and other moving engine components.

• Conductors should be supported throughout their length and should be secured at leastevery 46 cm (18 in.), using industry approved fasteners.

Electrical System

Page 8A-4 90-863758070 APRIL 2008

• All connections shall be in locations protected from the weather, in weatherproofenclosures or should be watertight. If connections are exposed to immersion, they mustbe watertight.

• Metals used for terminal studs, nuts, and washers shall be corrosion resistant andgalvanically compatible with the conductor and terminal lug. Aluminum and unplatedsteel shall not be used for studs, nuts, and washers.

• No more than 4 conductors shall be secured to any one terminal stud.• Only industry approved terminals shall be used, which typically include ring and captive

spade types.• Solder shall not be used as the sole means of mechanical connection in any circuit.

Solder connections shall be properly supported to minimize flexing of the solderconnection.

• Twist‑on connectors (i.e. wire nuts) shall not be used.• Wire size and insulation rating shall be selected in accordance with industry standards

with the proper overcurrent protection being used.

Battery and Battery Cables RequirementsNOTICE

Reversing the battery cables can damage the electrical system. Connect the positive leadto the positive terminal and the negative lead to the negative terminal.

! WARNINGImproper design and installation of the electrical system can result in serious injury ordeath. Adhere to all applicable marine regulations (United States Coast Guard [USCG],European Union–Recreational Craft Directive [EU‑RCD], etc.) and the standards theyreference (American Boat and Yacht Council [ABYC], Society of Automotive Engineers[SAE], International Standards Organization [ISO], etc.) for the market in which the boatwill be sold.

! CAUTIONDisconnecting or connecting the battery cables in the incorrect order can cause injuryfrom electrical shock or can damage the electrical system. Always disconnect thenegative (‑) battery cable first and connect it last.

BatteryIMPORTANT: Follow all applicable regulations or industry standards when installing thebattery. Ensure that the battery cable is installed so that it meets the pull test requirementsand that positive battery terminal is properly insulated.IMPORTANT: Some areas require that the battery be installed in an enclosed case. Referto regulations for your area.IMPORTANT: Always tighten battery cables with a wrench.Select a battery that meets these specifications:Use a 12‑volt marine type battery with tapered post or side‑terminal connectors. Don notuse a battery with wing nut connectors. Ensure that the battery capacity rating meets orexceeds the recommended cranking battery specifications.

Cranking Battery Specifications

Model Minimum required rating

Electrical System

90-863758070 APRIL 2008 Page 8A-5

All carburated models 375 cca / 475 mca / 90 AhAll MPI models 750 cca / 950 mca / 180 AhAll DTS Models 800 cca / 1000 mca / 190 Ah

Ensure that the battery has a reserve capacity rating that meets or exceeds the electricalaccessory loads of the particular application. Refer to applicable standards for calculationprocedure.• Install the battery according to the following specifications:• As close to the engine as possible.• In an accessible location for service.• Ensure that the battery compartment is properly vented in accordance with the industry

standards and regulations.• Ensure that the battery is not installed above or below a fuel tank, fuel filter, or fitting

in a fuel line.• Ensure that the battery is installed so that the metallic objects cannot come in contact

with the ungrounded (positive) battery terminal.• Ensure that the fuel system components within 30.5 cm (12 in.) and above the

horizontal plane of the battery top surface are shielded with dielectric material.• Ensure that the battery parts that are continuously energized, such as the positive

battery terminal and the cable connections are physically protected with boots or otherforms of protection to prevent accidental short circuits.

• Ensure that the battery cable connections are tight and protected with a batteryconnection sealant.

• The battery installation for multiple engine installations require special batteryconsiderations.

Battery CablesIMPORTANT: Battery cables must comply with SAE J1127 or comparable standards.• Select proper size positive (+) and negative (‑) battery cables using the chart.

Battery Cable Length RequirementsAverage Cable Length Cable Gauge

Up to 1.1 m (3‑1/2 ft.) 25 mm2 (4)

1.1–1.8 m (3‑1/2–6 ft.) 35 mm2 (2)

1.8–2.3 m (6–7‑1/2 ft.) 50 mm2 (1)

2.3–2.9 m (7‑1/2–9‑1/2 ft.) 50 mm2 (0)

2.9–3.7 m (9‑1/2–12 ft.) 70 mm2 (00)

3.7–4.6 m (12–15 ft.) 95 mm2 (000)

4.6–5.8 m (15–19 ft.) 120 mm2 (0000)

Refer to the following battery cable guidlines:• Multiple engine installations (including generator sets) require that a negative cable be

run between the engines. The cable must be of sufficient size to carry the highestcranking current that could be encountered.

• On applications with crossover (parallel) cranking motor circuits in multiple engineinstallations (including generator sets), a separate negative ground cable must be runbetween the engines (in addition to the cable mentioned above). The cable must besized to handle the highest possible load in the cranking circuit.

Electrical System

Page 8A-6 90-863758070 APRIL 2008

• Battery cables must be routed above normal bilge water levels throughout their length.• Battery cables must be routed to avoid contact with metallic fuel system components.• The positive battery cable must be routed to avoid contact with any portion of the engine

or drive train.• Cables that are exposed to physical damage should be protected by conduit, raceways,

tape, etc.• Cables that pass through bulkheads or other structural members should be protected

against chafing with grommets, etc.• To ensure good electrical contact, use only electrical grade (resin flux) solder when

soldering battery cable terminals to cable ends. Some form of mechanical connection(for example, by swaging or crimping) is also recommended, and is required if lengthof solder connection is less than 1‑1/2 times the diameter of the stranded area of thecable. See Multiple EFI Engine Battery Precautions.

Electrical ConnectionsRefer to the following precautions when working on or around the electrical harness, orwhen adding other electrical accessories, to avoid damage to the electrical system.• Do not tap accessories into the engine harness.• Do not puncture wires for testing (probing).• Do not reverse the battery leads.• Do not splice wires into the harness.• Do not attempt diagnostics without the proper, approved service tools.IMPORTANT: When routing all wire harnesses and hoses, ensure that they are routed andsecured to avoid potential contact with moving parts hot spots on the engine.

Tube Ref No. Description Where Used Part No.

25 Liquid Neoprene All electrical connections exceptthe battery 92- 25711 3

SmartCraft ProductA Mercury SmartCraft System instrument package can be purchased for this product. Afew of the functions the instrument package will display are engine RPM, coolanttemperature, water pressure, battery voltage, fuel consumption, and engine operatinghours.The SmartCraft Instrument package also aids in Engine Guardian diagnostics, bydisplaying critical engine alarm data and indicating potential problems.Refer to the Mercury SmartCraft Operator's Supplement for the warning functions andbasic operation of the SmartCraft instrument package. Refer to the instructions includedwith the instruments for installation instructions.

Engine HarnessGENERAL INFORMATION

Fuel injected MerCruiser engine models are SmartCraft ready and may be rigged usingthe SmartCraft instrumentation, analog instrumentation, or a combination of the two.If using anadapter, do not overtighten the clamp or deform the connector. Ensure that theconnection is oriented at angle or installed in a location that places the connection at riskfor exposure to moisture. Mount the connector with a downward slope of 30º from horizontalto provide additional protection from water intrusion. Ensure that the location does notinterfere with moving parts on the engine or boat.

Electrical System

90-863758070 APRIL 2008 Page 8A-7

The adpater limits accessory current through the boat harness to 15 amps, even if the boathas a 10‑pin harness that is capable of handling larger accessory loads.SmartCraft data is carried in the 14‑pin system without the use of a special data harness.SmartCraft data is not supported across the adapters. A separate CAN line will be neededon a boat using SmartCraft instrumentation and an adapter harness.

ENGINE HARNESS INSTALLATION

! CAUTIONFailure to protect wiring with an appropriate fuse can damage the wiring and start a fire.When installing any accesories, we recommend using a Mercury accessory kit. Alwaysuse the appropriate fuse to protect wiring.

Electrical System

Page 8A-8 90-863758070 APRIL 2008

IMPORTANT: The accessory wire in the 14‑pin harness will not support more than 15amps. The main power relay fuse may blow if an excess of 15 amps is applied. Refer to theMercury Precision Parts Accessories Guide for an optional accessory power relay kitthat will accommodate higher amperage draw.1. Route the instrumentation wiring harness back to the engine, making sure that the

harness does not rub or get pinched. If an extension harness is required, be sure tosecure the connection properly.

2. Fasten the harnesses to the boat at least every 45.7 cm (18 in.) , using appropriatefasteners.

3. Models with a 10‑pin harness, connect the instrumentation wiring harness to the engineharness plug. Secure the connection with the hose clamp.

4. Tighten the hose clamp to secure the wiring harness to the engine harness plug.5. Models with a 14‑pin harness, connect the instrumentation wiring harness to the engine

harness plug.a. Connect the depth transducer connector to the DLC/Depth transducer connector

on the engine harness.b. Connect the paddle wheel/tank level connector.c. Connect the power harness (Clean Power with 5‑amp fuse) connector (DTS and

PCM09 only).

a

bcd

e

12118

Typical 14‑pin DTS harnessa - Engine harness connectorb - Transmission harness connectorc - Paddle wheel/tank level connector

d - DLc/depth transducer connectore - Power harness connector/clean

power with 5‑amp fuse (DTS andPCM09 only)

Electrical System

90-863758070 APRIL 2008 Page 8A-9

Engine Connections

a

b

c

23629

a - Starter solenoidb - 90‑amp fuse

c - Positive (+) battery cable

NOTE: The negative (‑) battery wire can be connected to the port or starboard flywheelhousing ground stud.

a 20459

a - Negative (–) battery wire

Continuity Wire ConnectionIMPORTANT: Do not attach any accessory ground (–) wires to the transom plate groundpoint. Accessory ground wires can only be attached to the ground stud on the engine.IMPORTANT: Models equipped with a 14‑pin engine wiring harness are equipped with aseparate transom harness. Incorporated into the transom harness is a continuity circuitground lead. Proper ground connection between the transom and the engine is requiredto ensure proper operation of the corrosion protection system.

Electrical System

Page 8A-10 90-863758070 APRIL 2008

1. For models equipped with a 14‑pin engine harness, secure the transom harnesscontinuity circuit ground lead to the inner transom plate using the grounding screw onthe upper port side of the inner transom plate. Tighten the screw securely.

a

b

c

23598

a - Transom harness ground leadb - Grounding screw

c - Inner transom plate

2. If the transom plate has a continuity wire attached, it can be removed or attached tothe flywheel housing. Whether or not this additional continuity wire is used, thecontinuity wire in the transom harness must be connected to the continuity circuit at thetransom plate.

! WARNINGExcessive current load in the continuity wire may cause the potential for fire, leading toinjury or property damage. Do not connect the negative (‑) battery cable to the transomassembly.

IMPORTANT: Ensure that the continuity wire is connected between the engine and theinner transom plate. This lead is critical for the corrosion protection system to operateproperly, especially when the MerCathode is being used.• Do not connect the negative cable to other than the unpainted locations shown to

ensure good electrical contact.

NOTICEAn improperly secured positive (+) battery cable or accessory lead can stress starterterminals or damage the starter solenoid. Secure accessory leads and the positive batterycable to the boat.

• Secure cables to the boat using industry‑approved fasteners to prevent stressing thecable and terminals.

• Connections at the engine should be coated with liquid neoprene to prevent corrosion.• Battery connections should be coated with battery connection sealant to help retard

corrosion.

Electrical System

90-863758070 APRIL 2008 Page 8A-11

Accessories

! WARNINGImproper design and installation of the electrical system can result in serious injury ordeath. Adhere to all applicable marine regulations (United States Coast Guard [USCG],European Union–Recreational Craft Directive [EU‑RCD], etc.) and the standards theyreference (American Boat and Yacht Council [ABYC], Society of Automotive Engineers[SAE], International Standards Organization [ISO], etc.) for the market in which the boatwill be sold.

• Coat connections with liquid neoprene to prevent corrosion.

NOTICEAn improperly secured positive (+) battery cable or accessory lead can stress starterterminals or damage the starter solenoid. Secure accessory leads and the positive batterycable to the boat.

• Secure leads to the boat using industry‑approved fasteners to prevent stressing theleads and starter terminal.

• Refer to industry standards and regulations for additional information.

Audio Warning SystemAudio Warning System without Emissions Control

1. Place the large decal on the instrument panel, or another location where the operatocan see it easily.

ALARM INDICATES LOW OIL OR OVERHEATING

APPLY THE PROPER DECAL TO THE DASHBOARD OR OTHER APPROPRIATE LOCATION:

AUDIO WARNING HORN WILL SOUND WHEN: 1. ENGINE OIL PRESSURE IS TOO LOW 2. ENGINE TEMP. IS TOO HIGH, OR 3. DRIVE OIL LEVEL IS TOO LOW

TO TEST AUDIO WARNING HORN:TURN KEY TO "ON" POSITION (ENGINE OFF)

a

b

7799

a - Small decal (transparent)b - Large decal

2. Test audio warning system during pre‑delivery preparation section.Audio Warning System with Emissions Control

IMPORTANT: The audio warning system will indicate that a problem has occured. It doesnot protect the engine from damage.Your Mercury MerCruiser power package may be equipped with an audio warning system.Most faults cause the warning horn circuit to activate. How the warning horn activatesdepends on the severity of the problem.

Electrical System

Page 8A-12 90-863758070 APRIL 2008

There are three warning horn states:• Caution• Severe• Onboard Diagnostic Marine (OBDM) fault

CAUTIONIf a caution is detected, the audio warning system will sound for six one‑second intervals.

ON ON

OFF

ON

OFF

ON

OFF

ON

OFF

ON

OFF

1

1

1

1

1

1

1

1

1

1

1

OFF

33402

a

b

a - Horn (on or off)b - Time (in seconds)

Below are some examples of a caution fault:• Transmission fluid temperature is too hot• Drive oil is low• Sensor failure

SEVEREIMPORTANT: If you experience a severe fault, contact your authorized MercuryMerCruiser dealer.If a severe fault is detected, the audio warning system will sound for six seconds, turn offfor six seconds, then sound for six more seconds.

33403

aONON

6 6 6

OFF

b

a - Horn (on or off)b - Time (in seconds)

The following are examples of conditions that could trigger a sever fault:• Engine oil pressure is too low• Engine temperature is too hot• Seawater pressure is too low• Transmission pressure is low

Electrical System

90-863758070 APRIL 2008 Page 8A-13

OBDMIf an OBDM fault is detected, the audio warning system will sound for one five‑secondinterval, followed by a, 1/2‑second interval every 60 seconds for certain faults related tothe emissions or fuel system. See your authorized Mercury MerCruiser dealer forassistance.

33404

a

OFF

ON

5 60 60 60½ ½ ½

ON ON ON

OFF OFF

b

a - Horn (on or off)b - Time (in seconds)

TESTING THE AUDIO WARNING SYSTEM1. Turn the ignition switch to the "ON" position without cranking the engine.2. Listen for the audio alarm. The alarm will sound if the system is functioning correctly.

Multiple EFI Engine Battery PrecautionsSituation

Alternators: Alternators are designed to charge the battery that supplies electrical powerto the engine that the alternator is mounted on. When batteries for two different enginesare connected, one alternator will supply all of the charging current for both batteries.Normally, the other engine's alternator will not be required to supply any charging current.EFI Electronic Control Module (ECM): The ECM requires a stable voltage source. Duringmultiple engine operation, an onboard electrical device may cause a sudden drain ofvoltage at the engine's battery. The voltage may go below the ECM's minimum requiredvoltage. Also, the alternator on the other engine may now start charging. This could causea voltage spike in the engine's electrical system.In either case, the ECM could shut off. When the voltage returns to the range that the ECMrequires, the ECM will reset itself. The engine will now run normally. This ECM shut downusually happens so fast that the engine just appears to have an ignition miss.

RecommendationsBatteries: Boats with multi‑engine EFI power packages require each engine be connectedto its own battery. This ensures that the engine's electronic control module (ECM) has astable voltage source.Battery Switches: Battery switches should always be positioned so each engine is runningoff its own battery. DO NOT operate engines with switches in BOTH or ALL position. In anemergency, another engine's battery can be used to start an engine with a dead battery.Battery Isolators: Isolators can be used to charge an auxiliary battery used for poweringaccessories in the boat. They should not be used to charge the battery of another enginein the boat unless the type of isolator is specifically designed for this purpose.NOTE: Sure Power Industries Inc., Model 32023A meets this design specification.1. The boat may have 2 engines connected to a single Model 32023A battery isolator.2. The Model 32023A battery isolator is connected to 2 banks of batteries.3. Each bank contains 2 batteries with the cranking battery for 1 engine in each bank.4. The second battery in each bank is connected in parallel to the cranking battery.

Electrical System

Page 8A-14 90-863758070 APRIL 2008

5. The Model 32023A battery isolator is designed for this type of use; 2 battery banks, 2charging sources, 120 amps (maximum alternator output).

6. When the engines are running, either engine's alternator could be charging either bankof batteries through the Model 32023A battery isolator.

Any other manufacturer's battery isolator that is the same type as the Sure Power Inc.,Model 32023A could also be used.Generators: The generator's battery should be considered another engine's battery.

Battery Switch! WARNING

Improper design and installation of the electrical system can result in serious injury ordeath. Adhere to all applicable marine regulations (United States Coast Guard [USCG],European Union–Recreational Craft Directive [EU‑RCD], etc.) and the standards theyreference (American Boat and Yacht Council [ABYC], Society of Automotive Engineers[SAE], International Standards Organization [ISO], etc.) for the market in which the boatwill be sold.

A battery switch may be desirable to allow the power to be turned off when the boat is notin use and to allow switching between batteries in multiple battery applications. Certainindustry standard and regulations require the use of a battery switch and should beconsulted for requirements.• The intermittent rating of the switch shall not be less than the maximum cranking current

of the largest engine cranking motor that it serves.• The minimum continuous rating of the switch shall be the total of the ampacities of the

main overcurrent protection devices connected to the battery switch or the ampacity ofthe feeder cable to the switch, whichever is less (ABYC Standard).

• Connect the battery switch into the positive (+) battery cable as close to battery aspossible.

• The switch should be located in a readily accessible location for use in an emergency.• The switch should never be turned off while the engine is running to avoid damage to

the alternator. Switching between batteries should also be avoided while the engine isrunning (unless the switch has been specially designed for this purpose).

• The switch should not be used to connect multiple engines to one battery (or batterybank). See Multiple EFI Engine Battery Precautions.

Finding Other DiagramsNOTICE

Refer to the appropriate Mercury MerCruiser Diagram Binder for wiring diagrams or other diagrams not foundin this manual.

Power HarnessIMPORTANT: On all models equipped with DTS or Emissions Control you must install theappropriate power harness for your application. If your application is equipped with DTSand Emissions Control only one power harness is necessary.1. Connect the power harness to the battery. Ensure the lead with the fuse is installed

onto the positive battery terminal.2. Install the lead without the fuse onto the negative battery terminal.

Electrical System

90-863758070 APRIL 2008 Page 8A-15

3. Secure the battery cables and the power harness leads to the battery with hex nuts.Tighten the hex nuts to the specified torque.

Description Nm lb‑in. lb‑ftHex nut 13.5 120 –

4. Secure the power harness to the battery cable with a cable tie.

3711

Battery Isolator! WARNING

Improper design and installation of the electrical system can result in serious injury ordeath. Adhere to all applicable marine regulations (United States Coast Guard [USCG],European Union–Recreational Craft Directive [EU‑RCD], etc.) and the standards theyreference (American Boat and Yacht Council [ABYC], Society of Automotive Engineers[SAE], International Standards Organization [ISO], etc.) for the market in which the boatwill be sold.

You can install a battery isolator to charge of an auxiliary battery used to operate theaccessories. The battery isolator will allow the alternator to charge both the cranking batteryand auxiliary battery simulataneously, while preventing accessories connected to theauxiliary battery from discharging the cranking battery. The alternators used on MercuryMerCruiser products are equipped with a special external sensing circuit to ensure optimumcharging performance in these types of applications by compensating for the voltage dropacross the isolator.A special isolator is required for multiple engine installations where the cranking batteriesare to be charged from a common source. See Multiple EFI Engine BatteryPrecautions.IMPORTANT: Mercury MerCruiser cannot be responsible for problems resulting frominstallation of the isolator. The installer and the isolator manufacturer must ensure that theinstallation and any modifications to the Mercury MerCruiser product comply with allapplicable standards and regulations, including (but not limited to) wire size, type, routing,terminals, and overcurrent protection.

Electrical System

Page 8A-16 90-863758070 APRIL 2008

Battery Isolator Diagram

B2 A B1

OR

N

OR

NOR

N

OR

NPPL

PPL

RED

/PPL

RED

RED

BLK

BLK

BLK

BLK

BLK

RED

/PPL

a

b

c

d

a

b

e

d

f

24376

RED

BLK

a - Alternatorb - Starterc - Cranking battery

d - Ground stude - Auxiliary batteryf - Isolator

IMPORTANT: Cutting the orange wire flush with the wiring loom will result in damage tothe other wires in the loom.The splice wire must be a minimum of 8 AWG.1. Disconnect the orange wire from the alternator battery terminal. Splice the wire to the

orange wire and connect as shown.2. Insulate and seal the end of the wire with liquid neoprene and heat shrink tubing.